Noise on GPIO input pin

[yafisdamda]

Posted on April 25, 2016 at 19:16

Hi.

I am using STM32F030 for my product. The GPIOs are configured as input and are connected to touch ICs. Sometimes on some boards i observe noise on the input pins. I connected the pin to scope and i see the line continuously fluctuating. My knowledge to hardware is limited. I have no idea why it behaves this way. My hardware engineer is not able explain the behavior. I have 12 GPIO inputs connected to such ICs but only one or two behaves like this. That too not on all the boards. My GPIO init is

GPIO_InitStruct.Pin = GPIO_PIN_13;
GPIO_InitStruct.Mode = GPIO_MODE_INPUT;
GPIO_InitStruct.Pull = GPIO_NOPULL;
HAL_GPIO_Init(GPIOB, &GPIO_InitStruct);

plz help..!! Thanks!!

[Tesla DeLorean]

Posted on April 25, 2016 at 19:26

And is this coming from the Touch IC, rather than the STM32? Does it go away if you enable the pull up/down?

[yafisdamda]

Posted on April 25, 2016 at 19:29

Yes its coming from touch ic.

I have not enabled pull up/down. I will check that.

[Walid FTITI_O]

Posted on April 25, 2016 at 19:48

Hi yafis.mohamed,

I recommend the application note

http://www2.st.com/content/ccc/resource/technical/document/application_note/46/39/d6/92/4a/4d/40/9f/DM00087990.pdf/files/DM00087990.pdf/jcr:content/translations/en.DM00087990.pdf

'' Guidelines for designing touch sensing applications with surface sensors'' wich will be your support when developping using

http://www.st.com/web/en/catalog/tools/FM147/CL1794/SC961/SS1743/LN1734/PF258655

-Hannibal-

[yafisdamda]

Posted on April 25, 2016 at 19:55

No. Enabling pull up/down is not stopping it. 

Thanks!!!

[yafisdamda]

Posted on April 25, 2016 at 20:31

Any other suggestions?

May be the touch ic is behaving weird. But this only happens to one or two. Rest all work fine.Thanks..!!!

[Tesla DeLorean]

Posted on April 25, 2016 at 21:04

I don't know, I have no familiarity with your design.

If you remove the other IC does that fix it, how about if you replace it?

[re.wolff9]

Posted on April 26, 2016 at 11:07People here have confidence in the STM32 chips: If you configure a pin as an input, the STM will not make the pin fluctuate. So if your pin fluctuates and it is connected to the STM32 and another chip, it is that other chip that makes the signal fluctuate. When it happens on some boards and not on others, that's a hint that there is something like a bad soldering connection, or maybe you blasted the chips with ESD during soldering. Or possibly the chips need calibrating and they think you are almost close enough with your finger. 

[yafisdamda]

Posted on June 01, 2016 at 16:09

Hi. Sorry for the late response.

I too believe it is not the issue with STM32.The touch ic i am using is a auto-calibrating one. The part number is TTP223B.This behavior is observed after some time of power-on, like after a couple of hours.Thanks..!! 

[pierre23]

Posted on June 05, 2016 at 02:29

It's very hard to know what's wrong without having the full schematic and pcb layout. However, I would suggest two things:

 1) Try to change the IC. If it's behaving strangely after a few hours of usage, it might be faulty. Also, veryify that you're not using it out of the recommended operating conditions, as specified in the datasheet. Having a faulty IC isn't very likely, though.  2) Maybe you have a component which is affected by a temperature rise on your board and leads to high noise. But since I don't have more information on your design, I really can't know. You should also try using this IC with other MCUs, with an arduino, etc., and see in which conditions the phenomenon occurs. PS: a picture of this ''fluctuation'' would be handy.